Monolayer cell cultures offer certain distinct advantages compared to other in vitro systems: known long-term viability, feasibility for initiating many replicate cultures in any given experiment allowing the examination of many test conditions, and the uniform and extensive exposure of the cells to the incubation medium. Thus, islet cultures will be established from rat, pig, or human pancreas. We will study the effect of substances known to be stimulators, inhibitors, or modulators of islet hormone production in other systems. We will concentrate particularly on factors regulating glucagon and somatostatin synthesis and glucagon secretion. We will assess the possible mechanism of action of hormones trophic for islet secretion. A perfused islet cell culture system will be used in some of these studies. Rat islet cultures are used to establish the groundwork for these investigations. Pig and human islets are tested for their potential application to a hybrid artificial endocrine pancreas. We will measure the metabolism and growth of nondiabetic and diabetic human fibroblasts and the effect of potential regulatory factors such as insulin, hydrocortisone, ascorbate, glucose, and serum (including serum fractions). Insulin binding will be measured. The synthesis of collagen, membrane glycoproteins, and glycosaminoglycans by fibroblast cultures will be assessed in relationship to the clinical status of the donor and the growth characteristics of the cells. Cholesterol metabolism in relation to cell growth will also be measured. The possibility will be tested that alterations in glycoprotein, glycosaminoglycan, and cholesterol metabolism may lead to abnormal cell proliferation and function in diabetes. Thus, cultured cells are used to elucidate (1) factors that regulate islet hormone production, content, and secretion; (2) hormone action and binding; (3) cellular in vitro characteristics of diabetes; (4) protein and sterol constituents that may regulate cellular growth and metabolism.